[FFmpeg-devel] [PATCH] vc2enc_dwt: use 32 bit coefficients by default

Rostislav Pehlivanov atomnuker at gmail.com
Sat May 7 21:48:56 CEST 2016

On 7 May 2016 at 18:55, Christophe Gisquet <christophe.gisquet at gmail.com>

> 2016-05-07 19:12 GMT+02:00 Rostislav Pehlivanov <atomnuker at gmail.com>:

> > There is a slight performance drop associated with this change, making
> > the encoder slower by 1.15 times, however this is necessary in order to
> > avoid undefined behavior and overflows.
> This means no asm has been written yet. Is the performance drop mostly
> in transforms, or rather any coefficient manipulation (like rate
> evaluation etc), or memory bandwidth?
> In the former case, it might be less critical in the future.
 The costliest part of the encoder right now is encoding the coefficients
(~36%). Slightly less-costly is rate control (~31%), and after that is the
transform (~12%). There really isn't anything else, other than 3 copies
(input image converted to signed and copied to a buffer, then because the
transform is out of place there's a copy to another buffer and then back),
but they don't take that much time.

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